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d2cd9ede6e
Introduce MADV_WIPEONFORK semantics, which result in a VMA being empty
in the child process after fork. This differs from MADV_DONTFORK in one
important way.
If a child process accesses memory that was MADV_WIPEONFORK, it will get
zeroes. The address ranges are still valid, they are just empty.
If a child process accesses memory that was MADV_DONTFORK, it will get a
segmentation fault, since those address ranges are no longer valid in
the child after fork.
Since MADV_DONTFORK also seems to be used to allow very large programs
to fork in systems with strict memory overcommit restrictions, changing
the semantics of MADV_DONTFORK might break existing programs.
MADV_WIPEONFORK only works on private, anonymous VMAs.
The use case is libraries that store or cache information, and want to
know that they need to regenerate it in the child process after fork.
Examples of this would be:
- systemd/pulseaudio API checks (fail after fork) (replacing a getpid
check, which is too slow without a PID cache)
- PKCS#11 API reinitialization check (mandated by specification)
- glibc's upcoming PRNG (reseed after fork)
- OpenSSL PRNG (reseed after fork)
The security benefits of a forking server having a re-inialized PRNG in
every child process are pretty obvious. However, due to libraries
having all kinds of internal state, and programs getting compiled with
many different versions of each library, it is unreasonable to expect
calling programs to re-initialize everything manually after fork.
A further complication is the proliferation of clone flags, programs
bypassing glibc's functions to call clone directly, and programs calling
unshare, causing the glibc pthread_atfork hook to not get called.
It would be better to have the kernel take care of this automatically.
The patch also adds MADV_KEEPONFORK, to undo the effects of a prior
MADV_WIPEONFORK.
This is similar to the OpenBSD minherit syscall with MAP_INHERIT_ZERO:
https://man.openbsd.org/minherit.2
[akpm@linux-foundation.org: numerically order arch/parisc/include/uapi/asm/mman.h #defines]
Link: http://lkml.kernel.org/r/20170811212829.29186-3-riel@redhat.com
Signed-off-by: Rik van Riel <riel@redhat.com>
Reported-by: Florian Weimer <fweimer@redhat.com>
Reported-by: Colm MacCártaigh <colm@allcosts.net>
Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Kees Cook <keescook@chromium.org>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Drewry <wad@chromium.org>
Cc: <linux-api@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
73 lines
2.8 KiB
C
73 lines
2.8 KiB
C
#ifndef __ASM_GENERIC_MMAN_COMMON_H
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#define __ASM_GENERIC_MMAN_COMMON_H
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/*
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Author: Michael S. Tsirkin <mst@mellanox.co.il>, Mellanox Technologies Ltd.
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Based on: asm-xxx/mman.h
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*/
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#define PROT_READ 0x1 /* page can be read */
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#define PROT_WRITE 0x2 /* page can be written */
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#define PROT_EXEC 0x4 /* page can be executed */
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#define PROT_SEM 0x8 /* page may be used for atomic ops */
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#define PROT_NONE 0x0 /* page can not be accessed */
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#define PROT_GROWSDOWN 0x01000000 /* mprotect flag: extend change to start of growsdown vma */
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#define PROT_GROWSUP 0x02000000 /* mprotect flag: extend change to end of growsup vma */
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#define MAP_SHARED 0x01 /* Share changes */
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#define MAP_PRIVATE 0x02 /* Changes are private */
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#define MAP_TYPE 0x0f /* Mask for type of mapping */
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#define MAP_FIXED 0x10 /* Interpret addr exactly */
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#define MAP_ANONYMOUS 0x20 /* don't use a file */
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#ifdef CONFIG_MMAP_ALLOW_UNINITIALIZED
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# define MAP_UNINITIALIZED 0x4000000 /* For anonymous mmap, memory could be uninitialized */
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#else
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# define MAP_UNINITIALIZED 0x0 /* Don't support this flag */
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#endif
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/*
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* Flags for mlock
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*/
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#define MLOCK_ONFAULT 0x01 /* Lock pages in range after they are faulted in, do not prefault */
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#define MS_ASYNC 1 /* sync memory asynchronously */
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#define MS_INVALIDATE 2 /* invalidate the caches */
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#define MS_SYNC 4 /* synchronous memory sync */
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#define MADV_NORMAL 0 /* no further special treatment */
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#define MADV_RANDOM 1 /* expect random page references */
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#define MADV_SEQUENTIAL 2 /* expect sequential page references */
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#define MADV_WILLNEED 3 /* will need these pages */
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#define MADV_DONTNEED 4 /* don't need these pages */
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/* common parameters: try to keep these consistent across architectures */
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#define MADV_FREE 8 /* free pages only if memory pressure */
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#define MADV_REMOVE 9 /* remove these pages & resources */
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#define MADV_DONTFORK 10 /* don't inherit across fork */
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#define MADV_DOFORK 11 /* do inherit across fork */
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#define MADV_HWPOISON 100 /* poison a page for testing */
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#define MADV_SOFT_OFFLINE 101 /* soft offline page for testing */
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#define MADV_MERGEABLE 12 /* KSM may merge identical pages */
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#define MADV_UNMERGEABLE 13 /* KSM may not merge identical pages */
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#define MADV_HUGEPAGE 14 /* Worth backing with hugepages */
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#define MADV_NOHUGEPAGE 15 /* Not worth backing with hugepages */
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#define MADV_DONTDUMP 16 /* Explicity exclude from the core dump,
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overrides the coredump filter bits */
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#define MADV_DODUMP 17 /* Clear the MADV_DONTDUMP flag */
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#define MADV_WIPEONFORK 18 /* Zero memory on fork, child only */
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#define MADV_KEEPONFORK 19 /* Undo MADV_WIPEONFORK */
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/* compatibility flags */
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#define MAP_FILE 0
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#define PKEY_DISABLE_ACCESS 0x1
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#define PKEY_DISABLE_WRITE 0x2
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#define PKEY_ACCESS_MASK (PKEY_DISABLE_ACCESS |\
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PKEY_DISABLE_WRITE)
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#endif /* __ASM_GENERIC_MMAN_COMMON_H */
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